The present invention relates to the use of acoustic waves in the non-destructive testing of materials.
Methods and devices are known that utilize the propagation and reception of acoustic waves for testing characteristics of materials used in the formation of a variety of products, for example rotary wings, aircraft fuselages, nacelles, aircraft control surfaces, honeycomb sandwich structures, composite turbine fan blades, automotive passenger cells, automotive body panels, sailboat spars and masts, and boat hulls.
Carbon fiber-reinforced polymer (CFRP) materials and structures are of increasing importance in the aerospace, automotive, and other industries, due to their light weight and high strength. In modern aircraft, the fuselage and wings can be made from more than 50% composite materials, for example based on carbon fiber sheets and/or including sandwich structures formed by carbon fiber composite sheets disposed on opposing outer surfaces of an aluminum honeycomb center structure. As should be understood in this art, other composite structures may be used, for example formed by fiberglass sheets on opposing sides of a NOMEX core. The strength of such composite materials may be compromised by degradation caused, for example, by impact damage, fatigue, and thermal damage during service, as well as defects created by faulty manufacturing. Defects may include delamination of a composite sheet forming one or the other side of a sandwich structure or bond failure between a core material (for example, the aluminum honeycomb or NOMEX cores discussed above) and the outer composite sheets (disbonding). Such defects are often not identifiable by visual inspection.
To determine these defects in such materials, it is known to place a transducer on the material and strike the material with an impact hammer to thereby generate mechanical waves in the material that are detected by the transducer. The transducer outputs a corresponding signal to circuitry that digitizes the signal and converts the signal to the frequency domain, and a processor analyzes the resulting data for signal structures indicating a defect. It is also known to house a piezoelectric transducer in a hand-held housing so that when the housing is placed against the test material, a surface of the piezoelectric transducer abuts the outer surface of the test material. It is necessary to maintain the piezoelectric transducer in highly direct acoustic contact with the material surface, and an acoustic coupling gel may be disposed on the transducer surface and in direct contact with the material surface for this purpose. Upon the user's actuation of a controlling processor, the processor actuates the piezoelectric transducer, causing the transducer to impart an acoustic signal into the test material and the processor to receive a resulting signal from the output of the piezoelectric transducer. The processor analyzes the resulting signal to identify presence of defects in the material.
The present disclosure recognizes and addresses the foregoing considerations, and others, of prior art constructions and methods.